With the fast development of computer technology, multi-media apparatus is ever more widely used for displaying a rich plurality of contents, such as texts, sound, image and video. Correspondingly, projection apparatus capable of displaying big image finds wide applications and quick development. The inability of early stage projection systems to enable interaction between man and screen limits the scope of application, especially in the case of teaching in the classroom and game entertaining. This makes the need for interaction and real-life experience cannot be satisfied.
At present, there are two kinds of interactive projection systems at home and broad, which are technically mature, one is based on electronic whiteboard, and the other one employs interactive device. The former is designed with touch screen, infrared array, electromagnetic induction, and laser scanning, and other techniques. Albeit with high positioning dependability and precision, its dependence on specially made projection screens excludes the possibility of inter-operations on each projection plane, and results in inconvenience of installation and usage as well as high cost. By contrast, the projection system employing an interactive pen to position the pen point precisely via the interactive pens and the corresponding receivers, has no prerequisite for the projection plane, are capable of writing and touch operations in any projection plane, and are therefore receiving ever more attraction and affirmation.
The interactive projection system mainly consists of a control and processing unit, a memory unit, a projection unit, an image acquisition unit, and a projection plane, wherein the control and processing unit is connected via communication connections with the image acquisition unit, the projection unit, and the memory unit; the projection unit is employed for displaying image information on the projection plane; the image acquisition unit is employed for collecting image information on the projection plane and for transmitting the collected data information to the control and processing unit; the memory unit stores correction image, text data, correction formulas, and coordinate transformation programs.
An interactive projection system requires position correction before usage, and manual operation is the common currently adopted measure. The control and processing unit, subsequent to receiving a correction instruction, invokes correction data on the memory unit, and actuates the projection unit to project correction image onto the projection plane. The correction image on the projection plane has calibration points arranged in rectangular array mode, with one calibration point arranged in each of the four corners of the correction image, wherein the horizontal calibration points are spaced apart with a same distance, and the vertical calibration points are spaced apart with a same distance. The calibration points appear one by one (each correction image with one calibration point, with each of the plurality of correction image appears one by one; or each of the plurality of calibration points in a correction image appears one by one), and by employing an interactive pen to click these calibration points one by one manually, and to collect the absolute coordinate of each of the calibration point via the image acquisition unit, a manual position correction is realized, albeit being a low efficient correction wasting large amount of time and man power.
Another method of position correction is automatic correction, wherein the control and processing unit, after receiving a correction instruction, invokes a correction image in the memory unit or storage area of the computer connected with the projector. The correction image is shown in FIG. 1, with standard black squares arranged in rectangular array mode (with one black square at each of the four corners of the correction image, the horizontal black squares being spaced apart with a same distance, the vertical black squares being spaced apart with a same distance). The correction image is projected onto the projection plane by the projection unit, the positions of the black squares thereof are captured by the image acquisition unit, and their absolute coordinates on the projection plane are obtained, thereby arriving at a same effect as the manual correction with manual clicking with an interactive pen. Such a method of automatic correction is convenient, saves time, and increases the efficiency of position correction. However, compared with manual correction, the automatic correction has no means of knowing the starting position of the calibration points. Further, viewed from the coordinate system (the XY coordinate system) constructed by the horizontal centerline and the vertical centerline of the correction image, the black squares of the correction image are longitudinally and laterally symmetric, and hence with the employment of the automatic correction, the projected image is the same, regardless of whether the projector is placed on a desktop or hung up in the ceiling, or whether the projection system is front-projective or rear-projective; and therefore the installation mode of the projection system is not identifiable, resulting in incapability of precise positioning of the position of the interactive pen point.